alum

Definition

An astringent salt, usually occurring in the form of pale crystals, much used in the dyeing and tanning trade and in certain medicines, and now understood to be a double sulphate of potassium and aluminium (K₂SO₄·Al₂(SO₄)₃·24H₂O).

Etymology

From Middle English alum, alum, alym, alyme, from Anglo-Norman alum, alun, from Latin alūmen.

Example Sentences

• "Venice also needed alum for trade, since it was the point of departure for overland transportation of alum to southern Germany and its cloth-manufacturing Free Cities."
• "A natural astringent and antiseptic, potassium alum was coveted for its medicinal and cosmetic properties."
• "With weld and cochineal, which are colouring matters the most sensible to the action of sulphate of iron, the purified alums gave us colours more brilliant, fresh, and in a slight degree lighter; while those with our common alums were all duller, and evidently of a deeper hue."